The present invention relates generally to well bore equipment used in completion and workover of oil well and/or gas wells. Specifically, the invention relates to a continuous flow well washing tool and method for circulating fluids through well conduits and into surrounding formations for formation treatment.
Oil and gas wells are completed by installing a production casing into the hole from the surface and cementing the casing in place. After the production casing is installed, the casing is perforated at the producing depth and the oil and/or gas flows from the surrounding earthern formation through the casing perforations and up the production casing to the surface, usually through production tubing.
It is often necessary to treat the earthern formation which surrounds the perforated casing to enhance the flow of produced fluids. The treatment technique employed generally involves circulating water or an acid solution through the casing perforations, into the formation, and back up the casing string. Such washing of the formation allows loose sand to be flushed from the formation or consolidated, the creation of voids for improved gravel packing, and other techniques whereby fluid flow is improved in tight formations.
Various well washing tools are known in the art for packing of an area of the casing to allow fluid circulation. Such tools are usually lowered into the well bore on a tubing string at which point packers seal off the casing above and below the formation perforations, after which circulation of treating fluid is commenced. The treating fluid is usually circulated down the string supporting the wash tool, through the tool and out between the packers, and out the casing perforations into the formation. Flow then continues back into the casing through perforations above the packers allowing the returning fluid to flow upwardly through the casing above the wash tool.
Certain of the prior art wash tools were of the cup type packer arrangement. Cup type packers have been known to fail to adequately seal under conditions encountered in the well bore. Also, since the cup type packers engage the casing while the tool is being run into the well or pulled out of the well, they are sometimes torn or damaged during use.
One prior art wash tool included a tubular mandrel with packer assemblies carried on the mandrel at opposite ends thereof and an outer tubular body surrounding the mandrel between the packer assemblies. An annular chamber provided between the mandrel and the surrounding tubular body was in fluid comunication with the mandrel interior through ports in the walls of the mandrel. The tubular body was provided with ports which permitted fluid communication between the annular chamber and the exterior of the tool when a valve assembly carried in the annular chamber was actuated in response to a predetermined pressure increase. The packer assemblies were first set and then the valve assembly was actuated to provide fluid communication necessary for circulating fluids through the tool for washing the surrounding formation. The valving arrangement was not always reliable due to the presence of sand and other contaminants in the fluid being circulated through the valve.